In V8 release 4.9 we shipped more JavaScript ES2015 features than in any other previous release, bringing us to 91% completion as measured by the Kangax compatibility table (as of January 26). V8 now supports destructuring, default parameters, Proxy objects, and the Reflect API.

Release 4.9 also makes block level constructs such as class and let available outside of strict mode and adds support for the sticky flag on regular expressions and customizable Object.prototype.toString output.

Google’s proposes “use strong”; a subset of JavaScript that will allow V8 to enjoy some significant speed boosts

Like the restrictions in Strict Mode, Strong Mode aims to boost JavaScript performance. Some of the dynamic aspects of JavaScript hold back VM speed. Instead of “use strict”; it would be “use strong”; Strong Mode is actually a subset of Strict Mode.

The changes are still in the proposal stage but could have a bright future.

Restrictions in Strong Mode include accessing missing properties throw exceptions, arrays cannot be sparse, all scoping errors are static, and classes are immutable.

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Ken Snyder is a Software Craftsman specializing in PHP and JavaScript. Ken works in Salt Lake city for Right Intel.
He is the co-founder of UtahJS, an educational non-profit aimed at promoting JavaScript in Utah.